Three different projects have been initiated within the past year. Major emphasis has been on developing a modification of the classical electric dichroism experiment. This new technique, called photochemical electric dichroism, will allow a straight- forward determination of DNA wrapping, folding, or looping topology in DNA-protein complexes. It is basically a hybrid technique, uniting the methodology of electric dichroism with the sensitivity and selectivity of DNA footprinting techniques. The link is the formation of photochemical dimers between stacked pyrimidines, which is a marker for an absorption event. DNA helices can be cleaved chemically and enzymatically at the sites of these photodimers and probabilities analyzed by electrophoresis. Comparing frequencies of photodimer formation at a particular region between unoriented complexes and complexes oriented by an electric field gives the dichroism of the DNA at that region. We have recently visualized the loop of DNA in the DNA-DNA gyrase complex by this technique. Future experiments are planned for studying the structure of both bulk and active gene chromatin to deduce the effect of specific sequence protein binding on DNA structure. Statistically bent DNA is now thought to result from the juxtaposition of sequences of DNA with different base pair tilting properties. A project has been initiated toevaluate this proposal. A fragment of DNA with a biphasic B-A form transition has been uncovered. These two forms have very different base pair tilting and the rotational hydrodynamics of this fragment an the transition midpoint are consistent with a bent rod of DNA. We are now quantitating this effect. Finally, the sensitivity of rotational motion to molecular dimensions is allowing us to determine the structure and flexibility of Acanthameoba myosin II in a variety of structures, monomeric, dimeric, and bipolar filamentous, with both native and phosphorylated myosin.